linux-kernel - Re: [PATCH] x86: remove __phys_reloc

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Message-ID: <4C604F70.1040902@zytor.com>
Date:	Mon, 09 Aug 2010 11:56:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Namhyung Kim <namhyung@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] x86: remove __phys_reloc_hide

On 08/09/2010 01:07 AM, Ingo Molnar wrote:
> 
> * Namhyung Kim <namhyung@...il.com> wrote:
> 
>> remove unnecessary use of RELOC_HIDE(). It only does simple addition of ptr
>> and offset, and in this case, offset 0, does nothing. It does NOT do anything
>> with linker relocation things. I could find no reason to use it.
>>
>> The only user of __phys_reloc_hide() was __pa_symbol() so it can be removed
>> safely here.
>>
>> Signed-off-by: Namhyung Kim <namhyung@...il.com>
>> ---
>>  arch/x86/include/asm/page.h          |    5 ++---
>>  arch/x86/include/asm/page_32.h       |    1 -
>>  arch/x86/include/asm/page_64_types.h |    1 -
>>  3 files changed, 2 insertions(+), 5 deletions(-)
> 
> We do this as a general Voodoo barrier against GCC miscompilations.
> 
> You are right that it's largely moot by today (and especially so on x86 - i 
> only remember a single instance of miscompilation that Rusty mentioned few 
> years ago, and that was on powerpc), but the wrapper is simple enough, so 
> unless there's some real tangible improvement in the binary output we might as 
> well keep it.
> 
> Peter, what do you think?
> 

I agree... I suspect it might make some difference for gcc 3 stragglers.

	-hpa

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